Magnetic amplifier



1935- A. s. FITZ GERAtD 2,027,311

MAGNETIC AMPLIFIER Filed June 21, 1933 2 Sheets-Sheet 1 All // as? a/ INVENTOR.

Jan. 7, 1936. A, 5 F111 GERALD 2,027,311

MAGNETIC AMPLIFIER 2 SheetsSheet 2 Filed June 21, 1933 INVENTOR.

Glam. 53W

Patented Jan. 7, 1936 UNITED STATES PATENT OFFICE Application June 21, 1933, Serial No. 676,785 In Great Britain July 1, 1932 30 Claims.

This invention relates to magnetic amplifiers and more particularly to electric relay and control systems which are characterized by the circumstance that the electrical effect to be detected, or to which the electric control function is required to be responsive, is of a low order of magnitude.

In general, preferred engineering practice in electric relay and control problems provides such energy levels as are adequate to furnish ample electromagnetic forces, so that the apparatus employed may be characterized by substantial mechanical structure and especially by the avoidance of delicate parts and any necessity for accurate clearances or critical adjustments. Nevertheless, conditions are encountered, from time to time, increasingly so in recent years, wherein unavoidable limitations in the power available for operating control apparatus are involved. Examples of such problems may be found in such applications as remote control, especially by means of carrier current or superimposed audio frequency methods, temperature control, and other systems incorporating thermocouples, telemetering and other problems associated with electrical measuring instruments and the like; microphonic sound detecting systems; railroad and other signalling systems. Many other applications involving similar problems are well-known to those skilled in the art.

An outstanding example of such problems which is of notable importance at the present time in electrical and industrial engineering is represented by the rapid increase in the use of photo-electric apparatus in electrical control systems and industrial process control.

The magnitude of the electrical effects which may be derived from photo-sensitive elements is so minute that practical use can only be made of such apparatus when it is employed in connection with electron discharge amplifying systems or relays of an order of sensitivity associated more with the laboratory than with electrical power control equipment.

Very delicate relays or vacuum tubes, while both of these types of apparatus can be furnished in effective and reliable form, are more widely used at the present time in connection with communication services where this type of apparatus receives specialized maintenance service and is installed in buildings specially provided therefor, in which special conditions are maintained, which are more favorable to apparatus of this kind than is the case in the generality of electrical and industrial plants.

In spite of the manifold advantages which can be derived from the use of photo-electric apparatus, its application in electrical power systems and in manufacturing plants is greatly restricted on account of the fact that such apparatus requires specially qualified maintenance service and more frequent attention than is usually the case with equipment to which such institutions are accustomed.

In particular, the necessity for periodic testing and replacement of vacuum tubes precludes their use in many applications.

From the above brief discussion, it will be apparent that it would be a very great advantage if means might be provided which would bridge, in a more satisfactory manner, the gap between the energy level associated with photo-electric and other special effects and the prevailing general type of industrial control relays, contactors and associated equipment.

While several types of magnetic amplifiers are known in the art, apparatus of this type hitherto available has only been capable of amplifying substantial amounts of input power, for example, of the order of magnitude most conveniently expressed in watts or considerable fractions of a watt. Photo-electric cells, however, and other electrical effects of the type above referred to, are commonly associated with power levels which are more conveniently expressed in micro-watts.

It is accordingly an object of this invention to provide a power amplifying system capable of being responsive to energy levels of the order of magnitude associated with photo-electric cells and other effects of like smallness, and of stepping-up such effects to any desired magnitude so that powerful contactors or motor-actuated devices may be directly operated thereby.

It is a still further object of my invention to furnish apparatus for the purpose stated, which shall embody no devices calling either for special manufacturing methods or for maintenance service dificring from that required and generally available in connection with other common apparatus found in power systems and industrial plants.

It is yet a further object of my invention to provide apparatus of simple, cheap and reliable characteristics, and having great durability, which may be used instead of a vacuum tube amplifier in many engineering applications of photoelectric cells or other very low energy level devices, where the use of vacuum tubes is objected to on account of the necessity for frequent replacement.

The foregoing objects, and other objects appurtenant thereto, I accomplish through the agency of saturating reactors of the type wherein the amount of alternating current flowing in windings provided on the reactors is controlled by saturating the cores of the reactors by means of direct current excitation.

My invention comprises novel and, effective methods of employing such reactors in multistage arrangements whereby cumulative amplification up to any'desired extent, according to the number of stages used, is rendered possible.

According to my invention, alternating current energy derived from a saturating reactor, and controllable by a direct current applied to the reactor, is rectified and the resulting uni-directional current is applied to a further saturating reactor'so that the core of the second reactor is saturated with a direct current derived from the alternating current output of the first reactor. The alternating current output of the second reactor may likewise be rectified and, in the same manner, applied to a third reactor. In this manner, a catenated system embodying any desired number of reactors may be provided.

An important feature of my invention resides in the special compensating means which I have devised, whereby the direct current excitation applied to any such reactor embodied in such a catenated system, is proportional only to the direct current excitation applied to the preceding reactor. The magnetizing current drawn by a reactor when there is no direct current saturating effect applied thereto is caused to exercise no saturating effect upon the reactor which, in the catenated system, it precedes.

The novel features which I believe to be characteristic of my invention will be set forth with particularity in the appended claims. My invention itself. however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood with reference to the following description taken in connection with the accompanying drawings, in which Figure 1 is a diagrammatic view of an embodiment of my invention;

Fig. 2 is a diagrammatic view of a. modification of the embodiment of my invention shown in Fig. l, and

Fig. 3 is a diagrammatic view of a further modification of my invention.

In Fig. 1 I show a photo-electric cell i arranged to be afiected by a light effect (not shown) such as the intensity of daylight, or light from a source directed through a semiopaque medium such as smoke, liquid, etc., or any other type of photo-electric application. A contactor 2 has terminals 3 by means of which latter the contacts of the contactor may be included in any electrical control circuit (not shown) for the purpose of controlling a light= ing circuit, electric motor or any other eifect or device which it is desired should be controlled in accordance with the light impinging upon the photo-electric cell i..

For stepping-up the extremely small electric current furnished by the photo-electric cell i to an energy level necessary to operate the contactor 2, I show, in Fig. l, by way of example, a four-stage magnetic amplifier, in accordance with my invention, having input terminals 4 and output terminals 5. However, I wish it to be clearly understood that my invention is not limited to any definite number of stages; fewer aoazsn may be used if they will sufiice for the required purpose. Any number of additional stages may be added, arranged and connected in a similar manner, whereby the energy level may be stepped up, without limit, to any extent required. 5

In Fig. l the photo-electric cell i is energized from a suitable direct current source 6, and the circuits of my magnetic amplifier may be energized through terminals 1 from a source of alternating current 8 which may, for example, be 10 110 volts, 60 cycles. If desirable, I may provide, as shown, a transformer 9 for energizing, at a different voltage, the various circuits of my magnetic amplifier. The four-stage amplifier circuit shown in Fig. 1 includes four saturating 15 reactors I0, 20, 30, 40, each having magnetic cores ll, 2|, 3!, 4i; direct current saturating windings I2, 22, 32, 42, and reactance windings i3, 23, 33, 43. Associated with each saturating reactor, I provide rectlfiers I4, 24, 34, 44, which 20 may be of any suitable type, such as electrondischarge, vapor-electric, electrolytic, copper oxide, or other metallic contact type. I prefer to use a metallic contact rectifier of a type having good rectifying properties and low voltage 25 drop.

The photo-electric cell i, energized from the source 6, is connected in series with the saturating winding i2 of the reactor 10. The reactance winding l3 of the reactor Ill is energized with 30 alternating current in series with the rectifier Hi from the transformer 9.

With this arrangement, it will be apparent that when no photo-electric current flows in the winding l2, and accordingly there is no direct cur- I5 rent saturating efiect applied to the reactor ill,

a magnetizing current will be drawn by the reactor from the alternating current source, which magnetizing current will fiow in winding i3 and in the rectifier Hi. When photo-electric cur- 40 rent fiows in winding i2, whereby direct current saturation of the core Ill is set up, the current flowing in i3 and it will, in accordance with the magnitude of the photo-electric current, become augmented. The saturating winding 22 of 45 the reactor 20 is energized with the rectified cur rent from the rectifier i4. Direct current saturation of the core ii of the reactor 20 will, therefore, be in accordance with the magnitude of the alternating current flowing in i3 and it. The reactance winding 23 of the reactor 20 is likewise energized from the alternating current source in series with the rectifier 24 as are, in like manner, windings 33 and 43 and rectifiers 3d and id of the third and fourth stage reactors 55 30 and 30', respectively. The saturating winding 32 of reactor 30 is energized with rectified current from 26 and, in like manner, the saturating winding 52 of the reactor 40 is energized from the rectifier 34. 60

It will be seen, therefore, that the core i i of the first stage reactor i0 is saturated in accordance with the input to the amplifier which, in the pres ent case, is the current furnished by the photoelectric cell i. The saturating winding 22 of the second stage reactor 20 receives direct current proportional to the alternating current flowing in the reactance winding of the first stage reactor ii]. Likewise, the saturating winding 32 of the third stage receives direct current proportional to the alternating current drawn by the reactance winding 23 of the second stage reactor 20 and, in like manner, saturating winding 42 of the last stage reactor 40 receives direct current propor- 35 tional to the alternating current in the reactance winding 33 of the third stage reactor 30.

Rectifled current from the last stage rectifier 44 is connected to fiow in the operating coil of the contactor 2. The contactor 2, therefore, is energized with direct current proportional in magnitude to the alternating current flowing in the reactance winding of the last stage reactor.

Thus, in accordance with this arrangement, it will be readily seen that in my magnetic ampliher, the saturating windings of the second, third and fourth reactors receive direct current proportional to the alternating current flowing in the reactance winding of each of the preceding stages.

In order to secure a magnetic amplifying system capable of being extended to an indefinite number of stages, and of operating in a completely effective manner, no matter how many stages may be employed, I provide special compensating windings 25, 35, 45, situated on the reactors 20, 30, 40, respectively. The compensating windings 25, 35, 45 are wound co-axially with the direct current saturating windings 22, 32, 42 and are energized with direct current in series with rheostats 26, 36, 46, by means of a rectifier ll energized from the transformer secondary 8. The connections of the coils 25, 35, 45 are made so that the magnetizing effect, due to these coils, acts in opposition to the direct current magnetizing effect of the saturating coils 22, 32, 42.

The purpose of these coils is to compensate for the normal magnetizing current of the reactors. Obviously, the reactance windings i3, 23, 33, 43 will carry a magnetizing current when no direct current flows in the saturating windings i2, 22, 32, 42. The effect of direct current in the saturating windings will be to increase the current flowing in the reactance windings. The effect of the compensating windings 25, 35, 45 is to permit application to the reactor in each stage of a direct current saturating effect which shall be, not proportional to the current in the reactance winding of the preceding stage, but instead, proportional to the increase thereof due to the extent to which the preceding stage is saturated.

Referring, for example, to the first and second stage reactors I0 and 23, this effect is accomplished by adjusting the current in the compensating winding 25 by means of the rheostat 26 so that the direct current excitation set up by 25 is equal and in opposition to the ampere turns set up by the winding 22 due to the current flowing therein when no direct current is flowing in the first stage saturating winding l2. Thus, under this condition, the net direct current effect tending to saturate the core of 20 is zero. In practice, the current in 32 is observed when no D. C. saturating effect is applied to in and the rheostat is adjusted for minimum value of the current in 32.

If, now, a small direct current from the photosensitive element I be set up in i2, this will saturate the core of IO and will cause an increase in the alternating current flowing in l3 and in consequence, a corresponding increase in the rectified current flowing in 22. The effect of 22 and 25 will now be unequal and the core of 20 will be saturated to an extent dependent upon and substantially greater than the saturation of i0.

Thus, the effect of the compensating winding 25 is to cause the core of 20 to be saturated to an extent proportional to the difference between the current flowing in 22 when current flows in I2 and the lesser current which flows in 22 when the core of I0 is unsaturated, due to the absence of any current in i2. In other words, an amplifled saturating effect is applied to 20 which is substantially proportional to the degree of saturation of ID.

The windings 35 and 45 on reactors 30 and 40 serve precisely the same purpose in respect of the third and fourth stages. It will be clear from the above explanation that when proper adjustment of the compensating current is made in the windings 25, 35, 45, all the reactors are completely unsaturated when no current flows in l2. Thus, the effect of a current in I2 is to cause cumulative saturation of all four stages.

The importance of this compensating feature of my invention will be immediately apparent, if consideration be given, in comparison with the above explanation, to the conditions which would result if the windings 25, 35, 45 be omitted.

Under these circumstances, with no current in l2, the core of 20 would be partially saturated due to the magnetizing current in ill. This would cause a marked increase in the magnetizing current flowing in the winding 23. As a result, the core of 30 will be saturated to a still further extent causing, in like manner, a still greater increase in the magnetizing current flowing in the winding 33. Thus, the core of 40 would be even more strongly saturated than 30. As a result of this, it will readily be appreciated that not only would such an arrangement be inferior in sensitivity to the compensated system I have shown, but that, further, the number of possible stages is definitely limited. Since, as explained above, with no saturating current applied to the first stage at all, each of the successive stages is, nevertheless, subjected to an initial saturating effect, which is of increased extent in each succeeding stage, it is obvious that with more than a very limited number of stages, the cumulative effect of the magnetizing currents of the intermediate stages will result in complete initial saturation of the final stage under which condition the arrangement would be completely useless.

The importance of the compensating winding will be still further apparent if consideration be given to the conditions under which maximum effectiveness, or gain per stage, is obtained. The effective gain given by the first stage may be expressed by dividing the watts dissipated in the saturating winding l2 due to a given photo-electric current, into the difference between the watts developed in the winding 22 due to said photo electric current and the watts in winding 22 when there is no current in 92.

In order that the gain, as expressed above, may be a maximum, the resistance of 22 should be suitably matched with the characteristics of the reactor l0 and its winding l3, which value of resistance may readily be determined by experiment. The alternating current voltage derived from 9 should also be appropriately determined in relation to the permeability curve and characteristics of Ill. If the voltage of 9 be varied, it will be found that a fairly extended range of voltage exists within which approximately maximum gain can be obtained. Above and below this range, the gain decreases markedly.

A curve showing the relation between gain per stage and applied A. C. voltage would resemble, in general form, the permeability curve of the core material from which it is derived.

. applications.

It will be appreciated that the lower the voltage at which a saturating reactor, in the system shown in Fig. 1, be operated, the less will be the amount of magnetizing current flowing in the absence of any direct current saturation. It might be thought that if the reactors be worked at low voltages, such that the initial magnetizing currents are inappreciable multi-stage arrangements, without compensation, might give practical results. It is, therefore, important to realize that my investigations of this amplifying system have shown that the gain per stage is a maximum when an A. C. voltage is chosen, such that appreciable magnetizing current flows in the winding l 3 when there is no direct current saturation. The gain is a maximum when, with this value of A. C. voltage, the core of I is saturated by photo-electric current to such an extent that the current in i3 is increased in a ratio of the general order of magnitude of two to one. This being the case, it will be immediately apparent that the compensating windings are a material feature of the invention. Not only is the gain per stage greatly increased thereby but, in addition, due to the compensation effect, there is no limit to the number of stages which may be employed.

It will be observed that a compensating winding l5 has been shown on the first stage reactor Ill, despite the fact that there is no preceding stage, the magnetizing current of which need be compensated for. The winding may be omitted, if desired. However, it is frequently a convenience in view of the nature of photo-electric Some photo cells pass a definite amount of dark current. This dark current may be compensated for by adjustment of the rheostat l6 whereby increased efiectiveness and sensitivity may be obtained. Moreover, in many photo-electric applications, it is desired to secure operation of the control system when conditions depart from some predetermined intensity of illumination. In such cases, by adjustment of the rheostat 16, the core of Hi may be arranged to be completely unsaturated with any specific value of photo-electric current corresponding to the predetermined condition of illumination. Any change from this condition will then cause saturation of i0 and actuation of the contactor 2.

Should the source 8 be liable to appreciable variation of voltage, there may be corresponding changes in the magnetizing currents which flow, when there is no saturation of ill, in the windings i3, 23, 33, 33 of the reactors i0, 20, till, 60. It should be noted that since the compensating windings I5, 25, 35, 55 are also energized from the same source 3, through the rectifier Ill, an increase in the voltage will cause the compensating excitation likewise to increase and with reduced voltage the current in i5, 25, 35, 35 will, in a similar manner, be decreased, thus tending to maintain proper conditions of balance between the excitation of the compensating windings and the currents flowing in i2, 22, 32, 62, when there is no saturating effect applied to ill.

I have found that the arrangement as shown in Fig. 1 is completely satisfactory in this respect when operated from a source regulated within normal commercial limits. However, should it be desired to operate my invention from a voltage subject to unusually wide regulation, perfect compensation at all voltages may readily be secured by supplying rectifier H from the transformer 9 in series with a reactor l8 having a magnetic circuit and winding closely corresponding to the portion of a saturating reactor such as l9, 2!), 30 or 40, which is traversed by alternating current magnetic fiux. In other words, this special reactor may have a core dimensioned to correspond with the two middle legs only oi one of the saturating reactors I6, 20, 30 or 40, and windings similar to 13, 23, 33, 43. The variation in the magnetizing current, due to extreme voltage fluctuation, may be nonlinear with respect to such voltage change. The above arrangement furnishes congruent nonlinear variation in the currents in the compensating windings. If necessary, each compensating winding may be supplied from indiil ildual reactors and rectifiers similar to H3 and ever, for general use.

The operation of my invention will now be readily comprehended. With no saturating effect applied to I 0 and with proper adjustment of 26, 36 and 46, the cores of all of the reactors Ill, 20, 30 and 40 will be completely unsaturated. By adjusting the current in l5, by means of the Such refinements are not necessary, howrheostat l6, any photo-electric current in i2 likewise the rectified current in 22. The excitation, due to 22, now preponderates over 25, causing saturation of the core 20. Since the net output of the first stage-which, as explained previously, may be expressed as the watts developed in 22 due to the saturation of ill by the photo-electric current, minus the watts developed therein when i0 is unsaturated-will, due to the amplifying eifect of the saturating reactor ill, be many times the watts input into E2, the net D. C. ampere turns available to saturate 20 will likewise be substantially greater than the ampere turns applied to ill by the photo-electric current in i2. Accordingly, the saturating effect produced in 20 will be much greater than the saturation produced in I!) by the current in i2, and the output of 20, represented in a similar manner by the difference watts developed in 32, will be yet again amplified. In a similar way, the outputs of 30 and ll] will be of progressively increased amplitude.

Rectified output from the last stage is taken directly to the contactor 2. In this case, there will be some direct current in the coil of the contactor 2 when i0 is unsaturated due to the magnetizing current flowing in 53 under this condition.

When the photo-sensitive element l is stimulated by a light effect, the resulting saturating eifects set up in progressively amplified degrees in the several stages causes substantial saturation of Q0, and the current in the contactor coil will be increased substantially. The confactor 2 may, therefore, be adjusted so that the normal current, due to the magnetizing current of to, is substantially less than the drop-out value. When the photo-electric actuating effect is applied, the current in the coil may be caused to increase toa value substantially exceeding the pick-up value of 2 and the contactor is positively actuated t close its contacts. If the photo-electric efie ceases, the current will be reduced to below the drop-out value and the contactor will open the circuit.

The saturating reactors Ill, 20, 30, 40 are preferably of dissimilar type as shown in Fig. 1. The design of these reactors for the several stages is influenced by the following considerations.

Saturating reactors, such as are suitable for use in my magnetic amplifying system, usually consist of two interlinked magnetic systems, one carrying an alternating flux and the other car rying a direct flux, a common portion carrying both of these fluxes. Such reactors are preferably constructed so that there is no inductive relation, through this common portion, between the A. C. and D. C. exciting windings.

In carrying my invention into effect, I find it advantageous to use saturating reactors in which the relative proportions of the alternating and direct magnetic circuits are different, according to whether the reactors are used for the input, intermediate, or output stages in my magnetic amplifier.

The maximum output of a saturating reactor, forany given frequency, will be a function of the cross-section of the alternating portion of the magnetic circuit and of the number of turns in inductive relation therewith. Thus, in practice, for reasons of winding space, the maximum output tends also to be related to the length of the alternating portion of the magnetic circuit. By the expression maximum output reference is made to the maximum posrible difference which can be caused in the watts expended in a load circuit controlled by the reactor when the reactor is completely saturated, as compared with the condition when no D. C. saturation is applied.

Thus, in reactors of the type illustrated in Fig. 1, the maximum output will tend to be proportional to the cross-section and to the length of the two center legs of the reactors.

Thus, the dimensions of the middle legs of the reactor 40, which is used for the output stage, can be determined in accordance with the rated output for which the amplifying system is to be designed.

The amount of D. C. power required to saturate the last stage will be substantially less than the output power. Accordingly, the dimensions of the alternating magnetic circuit constituted by the two center legs of the reactor in the penultimate stage may be similarly determined since this should be capable of an output equal to the power required to saturate the last stage, plus losses in rectification.

In order to secure the maximum amplifying effect, it is clear that the reactors should be so proportioned that the alternating portions of the magnetic circuit can be raised to the saturation point with the minimum amount of direct current excitation. It is evident that the shorter be the length of the two center legs, the more readily will this part of the magnetic circuit be saturated. On the other hand, the direct current excited portion of the magnetic circuit is preferably made large in comparison with the alternating portion. The greater the length of the magnetic circuit comprising the solid portion of the center leg, the outer legs, and the horizontal portions joining these, the larger will be the window area of the core punching and the greater will be the space available for the DC saturating winding. The greater the winding space, the greater will be the excitation in ampere turns which can be produced per micro-watt of input power.

It may also be desirable to make the cross-section of the above-cited portion of the magnetic circuit substantially greater than that of the short center legs. If this be done, the magnetic potential gradient around the magnetic circuit which includes both outer and inner legs, may be made such that the constricted section. represented by the center legs constitutes very nearly the total magnetic reluctance of this magnetic path. Thus, the magnetizing force, or ampere turns per unit length, applied to the two center legs, will be equal to the saturating ampere turns divided by an effective length of magnetic path which will only very slightly exceed the length of the short center legs.

I show in Fig. 1 one method of proportioning the cores ll, 2|, 3|, ll of the four saturating reactors which I have found to be satisfactory. It will be noted that the cross-section and the length of the two center legs are progressively increased from the first to the last stages.

I have found that a reactor having core proportions similar to the first stage core ll, shown in Fig. 1, has satisfactory amplifying characteristics. If desired, all of the four reactors might be made, in increasing size, of similar proportions. However, I have shown in Fig. 1 all four reactors of like external dimensions. This gives somewhat reduced gain, per stage, in the latter stages, but is a convenient practical arrangement permitting standard size saturating coils for all stages, minimum tool expense in producing the core punchings, and a compact assembly.

I have found that the use of cores made of special nickel-iron alloys, such as those known to those skilled in the art by the trade name of permalloy is advantageous. Such alloys are characterized by a nickel content exceeding 75 percent. and by their property of being saturable with extremely low values of magnetizing force.

While the use of such material, throughout a multi-stage amplifier, would give increased effectiveness, I find it to be an economical and practical arrangement to employ permalloy only in the initial stage or stages, where the power level is low, and to employ ordinary magnetic material for the remaining and output stages where the power level is substantially higher.

In certain instances it may be found that the arrangement shown in Fig. 1, whereby the contactor 2 is operated directly from the last stage of the amplifier, may be unsuitable. Where it is desired to secure pick-up and dropout of a contactor, in accordance with the presence or absence of an illuminating effect, the arrangement shown in Fig. l in which, when the photo-electric effect is withdrawn, the current in the contactor is reduced to a value substantially less than the drop-out value, is entirely practical. However, cases may arise in which it is desired to secure characteristics such that the output is zero when the input is zero, and in which the output shall increase in accordance with the magnitude of the input.

For example, it may be desired to operate a motor directly from the output of the magnetic amplifier without the use of contacts in some environment in which open sparking may be inadmissible on account of fire risk or other reasons. It would be desirable, in such an instance, to pro- Vide that the energy delivered to the motor be reduced substantially to zero when the input to the amplifier is withdrawn.

Fig. 2 is a modification of my invention adapted to provide the above result.

In Fig. 2, I show the last stage only of an amplifier, which may consist of a plurality of stages, and in all other respects may be as shown in Fig. l. The last stage saturating reactor 50 has a saturating winding 52 and a reactance winding 53 similar to the arrangement shown in Fig. l.

The transformer 9 has a tap 56 which may desirably be adjustable and approximately in the neighborhood of the mid-point in the secondary winding.

I provide an additional reactor 55 having a. magnetic circuit closely corresponding to the portion of the reactor 50 which is traversed by alternating current magnetic flux. The reactor 55 may have a core dimensioned to correspond with the two middle legs of 50 and may have a winding of the same number of turns as the winding 53. Thus, with any given value of alternating current voltage applied to the reactor 55, the magnetizing current which would fiow in its winding would be precisely equal to the magnetizing current which would be drawn by the winding 53, if connected to the same A. C. voltage.

The reactors 50 and 55 are connected in series across the winding 9 so as to form a balanced bridge arrangement. The final stage rectifier 55 is connected between the tap 56 on the transformer winding 9 and the junction between the reactors 50 and 55. The tap on the transformer Q is adjusted so that the bridge is in balance when no net direct current saturating effect is applied to the reactor 50. Under this condition the potential of the junction will be substantially equal to that of the mid-point tap on the winding 9 and there will be substantially no alternating voltage applied to the rectifier 5 3.

The rectifier current from 5 3, which constitutes the output of the magnetic amplifier, I show in Fig. 2 connected to a power consuming device 5? which may be, for example, a motor.

Under the conditions cited, with no input to 82, all of the cores of the saturating reactors in the intermediate stages will be completely unsaturated, the bridge comprising 50 and 55 will be in a condition of balance and there will be no rectified output supplied to the motor which will thus remain stationary. If, now, photo-electric current from the photo-sensitive element i be caused to flow in the winding i2, causing saturation of it and still greater saturation of 50, the bridge will become unbalanced energizing rectifier 55 with alternating voltage. Thus, rectified current will be supplied to the motor which will operate at a speed depending upon the energization of i2 by the photo-cell i.

It will be obvious to those skilled in the art that the balanced bridge arrangement, by means of which direct current is applied to the motor 51, with compensation for magnetizing current effect, may be utilized for inter-stage magnetizing current compensation in place of the compensating windings 25, 35 and 45 in Fig. 1, if desired.

Thus, if Fig. 2 be supposed to represent an intermediate stage compensated in this way, 51 would represent the saturating winding, such as ,22, 32 or, in Fig. 1.

Likewise, it will also be obvious that I may use, instead of a tap on the transformer 9, a bridge circuit comprising the reactors 50 and 55, and two variable resistors or impedances, energizing the bridge from the transformer 9 and connecting the rectifier .54 across equi-potential points of the bridge.

While I have shown, by way of example, in Fig. 1 a magnetic amplifying system adapted to be energized by photo-electric current from the photosensitive element I, I wish it to be clearly understood that my magnetic amplifying system may be used in conjunction with any kind of electrical input effect whatever of such order of smallness as may render such amplifying means necessary. Furthermore, whereas the input effect in Fig. 1 is represented by a direct current, it will be obvious to those skilled in the art that the amplifier may be caused to actuate the contactor 2 in response to any alternating current input effect by providing an additional rectifier through which rectified current, derived from such an alternating current eifect, may be provided in the winding l2. For example, l2 may be energized with rectified current derived from a microphonic audio frequency effect whereby contactor 2 may be actuated in response to a tone signal.

While I have indicated that my magnetic amplifier may be operated from a source of volts, 60 cycles, in view of the fact that this is generally available, I wish it to be clearly understood that it is not limited to low frequency effects. It will be apparent to those skilled in the art that if the frequency of the source from which my magnetic amplifier is operated be increased, the effectiveness of the amplifier and the gain which may be obtained, will be increased in proportion to the increase in frequency.

It will likewise be apparent to those skilled in the art that my magnetic amplifier may be employed for amplifying alternating current effects provided the frequency of these effects be substantially less than the frequency of the source 8. For example, the amplifier may be energized from a source of super-audio frequency and the unidirectional current applied to the winding 12 may be modulated with audible frequency.

I show in Fig. 3 an arrangement suitable for amplification of audible effects by means of my invention.

In Fig. 3 I show two complete magnetic amplifiers 60 and 600, each of which may be substantially similar to the arrangement shown in Fig. 1, having input terminals 4, output terminals 5 and power supply terminals 3, all as shown in Fig. 1. Both these amplifiers are energized through terminals from a source of alternating power a which may be of a frequency substantially higher than the frequency of the effect which it is desired to amplify.

The alternating current effect to be amplified is applied to terminals 64. The input connections of the two magnetic amplifiers 60 and son are energized in parallel, through oppositely connected rectifiers 6i and 62 from the input terminals 64. The output terminals 5 of the amplifiers 60 and 600 are likewise connected in parallel, in opposite sense, to supply a load or output circuit 65.

With this arrangement, when an alternating effect is applied to the terminals 63, due to the oppositely connected rectifiers 6i and 62, the input windings 4 of 60 and 600 will be energized alternately in response to successive positive and negative half cycles of the input effect. Accordingly, the output delivered at terminals 5 by the amplifiers 60 and 600 will consist of alternate amplified intermittent uni-directional impulses corresponding to the half cycles applied to the input terminals 4. The terminals 5 being connected in opposite sense to the load 65, these half cycles will be combined so as to supply amplified alternating current to the load 65.

Although I have chosen a particular embodiment of my invention for purpose of explanation, many modifications thereof will be apparent to those skilled in the art to which it pertains. My invention, therefore, is not to be limited except insofar as is necessitated by the prior art and the spirit of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A magnetic amplifier comprising a plurality of saturable core devices connected in cascade, each having a saturating winding and an output winding, a source of control current connected to the saturating winding of the first of said devices, means for energizing said output windings, a circuit including rectifying means interconnecting the output winding of each device with the saturating winding of the next successive device, a controlled circuit connected to the output winding of the last of said devices, and means for substantially eliminating the effect on the controlled circuit of the magnetizing current of any of said devices, but the last, when unsaturated, comprising means associated with each device after the first for neutralizing the saturation thereof due to the magnetizing current of the preceding device.

2. A magnetic amplifier comprising a plurality of saturable core devices connected in cascade, each having a saturating winding and an output winding, a source of control current connected to the saturating winding of the first of said devices, means for energizing said output windings, a circuit including rectifying means interconnecting the output winding of each device with the saturating winding of the next successive device, a controlled circuitconnected to the output winding of the last of said devices, and means for substantially eliminating the effect on the controlled circuit of the magnetizing current of any of said devices, but the last, when unsaturated, comprising a compensating saturating winding for each of said devices after the first and means for energizing said compensating windings with current of such value that the M. M. F. of each is equal and opposite to that due to the magnetizing current of the preceding device.

3. A magnetic amplifier comprising a plurality of saturable core devices connected in cascade, each having a saturating winding and an output winding, a source of control current connected to the saturating winding of the first of said devices, means for energizing said output windings, a circuit including rectifying means interconnecting the output winding of each device with the saturating winding of the next successive device, a controlled circuit connected to the output winding of the last of said devices, and means for substantially eliminating the effect on the controlled circuit of the magnetizing current of any of said devices, but the last, when unsaturated, comprising a compensating saturating winding for each of said devices after the first, further rectifying means for energizing said compensating windings with uni-directional currents, and means for adjusting the value of said currents so that the M. M. F. of each of said compensating windings is equal and opposite to that due to the magnetizing current of the preceding device.

4. A magnetic amplifier comprising a plurality of saturable core devices connected in cascade, each having a saturating winding and an output winding, a source of control current connected to the saturating winding of the first of said devices, means for energizing said output windings, a circuit including rectifying means interconnecting the output winding of each device with the saturating winding of the next successive device, a controlled circuit connected to the output winding of the last of said devices, and means for substantially eliminating the effect on the controlled circuit of the magnetizing current of any of said devices, but the last, when unsaturated, comprising means associated with each device after the first for neutralizing the saturation thereof due to the magnetizing current of the preceding device, at least one of said saturable core devices having a core made of a nickel alloy capable of being raised substantially to saturation point by a magnetizing force of less than one Gilbert per centimeter.

5. A magnetic amplifier comprising a plurality of saturable core devices connected in cascade, each having a saturating winding and an output winding, a source of control current connected to the saturating winding of the first of said devices, means for energizing said output windings, a circuit including rectifying means interconnecting the output winding of each device with the saturating winding of the next successive device, a controlled circuit connected to the output winding of the last of said devices, and means for substantially eliminating the effect on the controlled circuit of the magnetizing current of any of said devices, but the last, when unsaturated, comprising means associated with each device after the first for neutralizing the saturation thereof due to the magnetizing current of the preceding device, the saturable core devices in the several stages having cores so proportioned that the magnetic circuit which is traversed by alternating current magnetic fiux is of increased dimensions in successive stages.

6. A magnetic amplifier comprising a plurality of saturable core devices connected in cascade, each having a saturating winding and an output winding, a source of control current connected to the saturating winding of the first of said devices, means for energizing said output windings, a circuit including rectifying means interconnecting the output winding of each device with the saturating winding of the next successive device, a controlled circuit connected to the output winding of the last of said devices, and means for substantially eliminating the effect on the controlled circuit of the magnetizing current of any of said devices, but the last, when unsaturated, comprising means associated with each device after the first for neutralizing the saturation thereof due to the magnetizing current of the preceding device, at least one of the saturable core devices having a core so proportioned that the length of the magnetic circuit traversed by direct current flux is substantially greater than the length of the magnetic circuit which is traversed by the alternating current flux.

7. A magnetic amplifier comprising a plurality of saturable core devices connected in cascade, each having a saturating winding and an output winding, a source of control current connected to the saturating winding of the first of said devices, means for energizing said output windings, a circuit including rectifying means interconnecting the output winding of each device with the saturating winding of the next successive device, a controlled circuit connected to the output winding of the last of said devices, and means for substantially eliminating the effect on the controlled circuit of the magnetizing current of any of said devices, but the last, when unsaturated, comprising means associated with each device after the first for neutralizing the saturation thereof due to the magnetizing current of the of saturablecore devices connected in cascade,

each having a saturating winding and an output winding, a source of control current connected to the saturating winding of the first ofsaid devices, means for energizing said output windings, a circuit including rectifying means interconnecting the output winding of each device with the saturating winding of the next successive device, a controlled circuit connected to the output winding of the last of said devices, and means for substantially eliminating the efiect on the controlled circuit of the magnetizing current of any of said devices, but the last, when unsaturated, comprising means associated with each device after the first for neutralizing the saturation thereof due to the magnetizing current of the preceding device, at least one of the saturable core devices having a core made of a nickel alloy capable of being raised substantially to saturation point by a magnetizing force of less than one Gilbert per centimeter, and at least one of the saturable core devices having a core made of steel.

9. A magnetic amplifier comprising a plurality of saturable core devices connected in cascade, each having a saturating winding and an output winding, a source of control current connected to the saturating winding of the first of said devices, means for energizing said output windings, a circuit including rectifying means interconnecting the output winding of each device with the saturating winding of the next successive device, a controlled circuit connected to the output winding of the last of said devices, and means for substantially eliminating the effect on the controlled circuit of the magnetizing current of any of said devices, when unsaturated, comprising means associated with each device after the first for neutralizing the saturation thereof due to the magnetizing current of the preceding device, said last mentioned means being characterized in that they do not involve inter-stage power losses and corresponding reduction in the efiective gain per stage.

10. A magnetic amplifier comprising a plurality of saturable core devices connected in cascade, each having a saturating winding and an output winding, a source of control current connected to the saturating winding of the first of said devices, means for energizing said output windings, a circuit including rectifying means interconnecting the output wnding of each device with the saturating winding of the next successive device, a controlled circuit connected to the output winding of the last of said devices, and means for substantially eliminating the effect on the controlled circuit of the magnetizing current of any of said devices, but the last, when unsaturated, comprising a compensating saturating winding for each of said devices after the first, together with means whereby, when, due to voltage variation, the magnetizing current of the preceding device is changed, the current in said compensating winding is commensurately changed.

11. A magnetic amplifier comprising a plurality of saturable core devices connected in cascade, each having a saturating winding and an output winding, 9. source of control current connected to the saturating winding of the first 10 of said devices, means for energizing said output windings, a circuit including rectifying means interconnecting the output winding of each device with the saturating winding of the next successive device, a controlled circuit connected to the output winding of the last of said devices, and means for substantially eliminating the effect on the controlled circuit of the magnetizing current of any of said devices, but the last, when unsaturated, comprising a compensating saturating winding for each of said devices after the first, rectifying means for energizing said compensating windings with current of such value that the M. M. F. of each is equal and opposite to that due to the magnetizing current of the preceding device, a further saturable core device having magnetic characteristics related to those of the preceding device, and means for energizing said further rectifying means in accordance with the magnetizing current drawn by said last mentioned saturable core device whereby, when, due to its voltage variation, the magnetizing current of the preceding device is changed, the current in said compensating winding is commensurately changed. 12. In combination, a source of alternating current, a first saturable core device having an alternating current winding, energized from said source, and a direct current saturating winding, means for supplying current to said direct current winding, rectifying means effectively connected to said alternating current winding, a second saturable core device having an alternating current winding, energized from said source, and a direct current saturating winding, said direct current winding being energized from said rectifying means, a circuit energized in accordance with an electrical condition of said second mentioned alternating current winding, a second rectifier, energized from said alternating current source, and a further direct current winding energized from said second rectifier and connected to oppose the saturating effect of said second mentioned direct current saturating winding, said last named direct current winding being so proportioned that its M. M. F. is substantially equal to that due to the magnetizing current in the alternating current winding of said first mentioned saturable core device when no direct current excitation is applied thereto.

13. In combination, a source of alternating current, a first saturable core device having an alternating current winding, energized from said source, and a direct current saturating winding, means for supplying current to said direct cur- 05 rent winding, rectifying means effectively connected to said alternating current winding, a second saturable core device having an alternating current winding, energized from said source, and a. direct current saturating winding, said 70 direct current winding being energized from said rectifying means, a circuit energized in accordance with an electrical condition of said second mentioned alternating current winding, a further direct current winding co-axial with said 76 second mentioned direct current saturating winding, and means for supplying to said last mentioned winding a direct current of such value that the magnetic eifect thereof is in opposition and is substantially equal to the magnetic effect" of the rectified current which flows in said second mentioned direct current saturating winding when no direct current saturating effect is applied to said first mentioned saturable core device.

14. In combination, a source of alternating current, a first saturable core device having an alternating current winding, energized from said source, and a direct current saturating winding, means for supplying current to said direct current winding, rectifying means effectively connected to said alternating current winding, 9. second saturable core device having an alternating current winding, energized from said source, and a direct current saturating winding, said direct current winding being energized from said rectifying means, a circuit energized in accordance with an electrical condition of said second mentioned alternating current winding, a further direct current winding co-axial with said second mentioned direct current saturating winding, and means for supplying to said last mentioned winding a direct current of such value that the magnetic eifect thereof is in opposition and is substantially equal to the magnetic effect of the rectified current which fiows in said second mentioned direct current saturating winding when no direct current saturating effect is applied to said first mentioned saturable core device, at least one of said saturable core devices having a core made of a nickel alloy capable of being raised substantially to saturation point by a magnetizing force of less than one Gilbert per centimeter.

15. In combination, a source of alternating current, a first saturable core device having an alternating current winding, energized from said source, and a direct current saturating winding, means for supplying current to said direct current winding, rectifying means effectively connected to said alternating current winding, 9. second saturable core device having an alternating current winding, energized from said source, and a direct current saturating winding, said direct current winding being energized from said rectifier, a circuit energized in accordance with an electrical condition of said second mentioned alternating current winding, and a further direct current winding opposing the effect of said second mentioned direct current winding, and means for energizing said last mentioned winding, said last named direct current winding being so proportioned that its M. M. F. is substantially equal to that due to the magnetizing current in the alternating current winding of said first mentioned saturable core device when no direct current excitation is applied thereto, at least one of the saturable core devices having a magnetic core so proportioned that the length of the magnetic path of the portion traversed by direct current fiux is substantially greater than the length of the magnetic circuit which is traversed by the alternating current fiux.

16. In combination, a source of alternating current, a first saturable core device having an alternating current winding, energized from said source, and a direct current saturating winding, means for supplying current to said direct current winding, rectifying means effectively connected to said alternating current winding, a second saturable core device having an alternating current winding, energized from said source, and a direct current saturating winding, said direct current winding being energized from said rectifying means, a circuit energized in accordance with an 5 electrical condition of said second mentioned alternating current winding, a further direct current winding opposing the effect of said second mentioned direct current winding, and means for energizing said last mentioned winding, said 10 last named direct current winding being so proportioned that its M. M. F. is substantially equal to that due to the magnetizing current in the alternating current winding of said first mentioned saturable core device when no direct current excitation is applied thereto, at least one of the saturable core devices being so proportioned that the cross-section of the magnetic circuit traversed by the direct current flux is substantially greater than the cross-section of the magnetic circuit which is traversed by the alternating current flux.

17. In combination, a source of alternating current, a first saturable core device having an alternating current winding, energized from said 25 source, and a direct current saturating winding, means for supplying current to said direct current winding, rectifying means effectively connected to said alternating current winding, a second saturable core device having an alternating 30 current winding, energized from said source, and a direct current saturating winding, said direct current winding being energized from said rectifying means, a circuit energized in accordance with an electrical condition of said second mentioned alternating current winding, a second rectifier energized from said alternating current source, and a further direct current winding energized from said second rectifier and connected to oppose the saturating eflfect of said second mentioned direct current saturating winding, said last named direct current winding being so proporiioned that it produces a substantially constant magnetomotive force equal to that due to a substantially constant saturating effect which 45 it is not desired should influence said second saturable core device.

18. In combination, an alternating current supply circuit, a saturable core device having an alternating current winding and a direct current 50 saturating winding, means for supplying current to said direct current winding, means for energizing said alternating current winding from said supply circuit, an electro-magnetic device having a first direct current exciting winding and a second direct current exciting winding, rectifying means, means effectively connecting said rectifying means to said alternating current winding, means for energizing said first exciting winding with uni-directional current from said rectifying 60 means, means actuated in accordance with the magnetization of the core of said electro-magnetic device, a. second rectifying means energized from said alternating current supply circuit, means for energizing said second exciting winding with unidirectional current from said second rectifying means so as to oppose the magnetizing effect of said first exciting winding, said last named exciting winding being so proportioned that the magnetomotive-force thereby applied to said 70 electro-magnetic device is substantially equal to is applied thereto. 75

19. In combination, a source of alternating current, a first saturable core device having an alternating current winding, energized from said source, and a direct current saturating winding, means for producing very small amounts of electrical energy not exceeding one hundred microwatts, means for supplying current from said means to said direct current winding, rectifying means efiectively connected to said alternating current winding, a second saturable core device having an alternating current winding, energized from said source, and a direct current saturating winding, said direct current winding being energized from said rectifying means, together with a circuit energized in accordance with an electrical condition of said second mentioned alternating current winding, at least one of said saturable core devices having a magnetic core made of nickel alloy capable of being raised substantially to saturation point by a magnetizing source of less than one Gilbert per centimeter.

20. In combination, a source of alternating current, a first saturable core device having an alternating current winding, energized from said source, and a direct current saturating winding, means for producing very small amounts of electrical energy not exceeding one hundred microwatts, means for supplying current from said means to said direct current winding, rectifying means efiectively connected to said alternating current winding, a second saturable core device having an alternating current winding, energized from said source, and a direct current saturating winding, said direct current winding being energized from said rectifying means, together with a circut energized in accordance with an electrical condition of said second mentioned alternating current winding, at least one of said saturable core devices having a magnetic core made of nickel alloy capable of being raised substantially to saturation point by a magnetizing force of less than one Gilbert per centimeter, at least one of said saturable core devices having a magnetic core so proportioned that the length of the magnetic circuit traversed by direct current fiux is substantially greater than the length of the magnetic circuit which is traversed by the alternating current flux, and at least one of the saturable core devices being so proportioned that the crosssection of the magnetic circuit traversed by-direct current flux is substantially greater than the cross-section of the magnetic circuit which is traversed by alternating current flux.

21. In combination, an alternating current supply circuit, a first saturable core device hav-' ing an alternating current winding and a direct current saturating winding, means for supplying current to said direct current winding, rectifying means, a core having magnetic characteristics similar to those of a portion of said first saturable 1 core device, a winding on said core, a bridge circuit including said winding and the alternating current winding of said first saturable core device, means for energizing said bridge circuit from said alternating current supply circuit across one diagonal, means for energizing said rectifying means from another diagonal of said bridge,

' means for causing said bridge to be balanced when no direct current excitation is applied to said first saturable core device, a second saturable core device having an alternating current winding and a direct current saturating winding, means for energizing said second alternating current winding from said supply circuit, means for energizing said second mentioned direct current saturating winding from said rectifying means, an output circuit and means for energizing said output circuit in accordance with an electrical condition of said last mentioned alternating current winding, whereby said second saturable core device is caused to re- 5 ceive saturating excitation proportional to the diiierence between the alternating current fiowing in said first-mentioned saturable core device when said first mentioned device is subjected to a. direct current saturating effect and the alter- 10 nating current flowing therein when no direct current saturating effect is applied thereto.

22. In combination, an alternating current supply circuit, a first saturable core device having an alternating current winding and a direct 15 current saturating winding, means for supplying current to said direct current winding, rectifying means, a core having magnetic characteristics similar to those of a portion of said first saturable core device, a winding on said core, a bridge cir- 20 cuit including said winding and the alternatingcurrent winding of said first saturable core device, means for energizing said bridge circuit from said alternating current supply circuit across one diagonal, means for energizing said 25 rectifying means from another diagonal of said bridge, means for causing said bridge to be balanced when no direct current excitation is applied to said first saturable core device, a second: saturable core device having an alternating curac rent winding and a. direct current saturating winding, means for energizing said second alternating current winding from said supply circuit, means for energizing said second mentioned direct current saturating winding from said rectifying means, an output circuit, and means for energizing said output circuit in accordance with an electrical condition of said last mentioned alternating current winding, whereby said second saturable core device is caused to receive 40 saturating excitation proportional to the difference between the alternating current flowing in said first mentioned saturable core device when said first mentioned device is subjected to a direct current saturating efiect and the alternating 45 current flowing therein when no direct current saturating effect is applied thereto, at least one of said saturable core devices having a core made of a nickel alloy capable of being raised substantially to saturation point by a magnetizing Gil force of less than one Gilbert per centimeter.

23. In combination, an alternating current sup ply circuit, a first saturable core device having an alternating current winding and a direct current saturating winding, means for supplying 55 current to said direct current winding, rectifying means, a core having magnetic characteristics similar to those of a portion of said first saturable core device, a winding on said core, a bridge circuit including said winding and the alternating 60 current winding of said first saturable core device, means for energizing said bridge circuit from said alternating current supply circuit across one diagonal, means for energizing said rectifying means from another diagonal of said bridge, 65 means for causing said bridge to be balanced when no direct current excitation is applied to said first saturable core device, a second saturable core device having an alternating current winding and a direct current saturating winding, 70 means for energizing said second alternating current winding from said supply circuit, means for energizing said second mentioned direct current saturating winding from said rectifying means, an output circuit, and means for energizing said 75 output circuit in accordance with an electrical condition of said la: 1 mentioned alternating cur-,"

rent winding, whereby said second saturable core device is caused to receive saturating excitation proportional to the difference between the alternating current flowing in said first mentioned saturable core device when said first mentioned device is subjected to a direct current saturating effect and the alternating current flowing therein when no direct current saturating effect is applied thereto, at least one of the saturable core devices having a magnetic core so proportioned that the length of the magnetic circuit of .the portion traversed by direct current flux is substantially greater than the length of the magnetic circuit which is traversed by the alternating current flux.

24. In combination, an alternating current supply circuit, a first saturable core device having an alternating current winding and a direct current saturating winding, means for supplying current to said direct current winding, rectifying means, a core having magnetic characteristics similar to those of a portion of said first saturable core device, a winding on said core, a bridge circuit including said winding and the alternating current winding of said first saturable core device, means for energizing said bridge circuit from said alternating current supply circuit across one diagonal, means for energizing said rectifying means from another diagonal of said bridge, means for causing said bridge to be balanced when no direct current excitation is applied to said first saturable core device, a second saturable core device having an alternating current winding and a direct current saturating winding, means for energizing said second alternating current winding from said supply circuit, means for energizing said second mentioned direct current saturating winding from said rectifying means, an output circuit, and means for energizing said output circuit in accordance with an electral condition of said last mentioned alternating current winding, whereby said second saturable core device is caused to receive saturating excitation proportional to the difference between the alternating current flowing in said first mentioned saturable core device when said first mentioned device is subjected to a direct current saurating effect and the alternating current flowing therein when no direct current saturating effect is applied thereto, at least one of the saturable core devices being so proportioned that the cross-section of the magnetic circuit traversed by the direct current flux is substantially greater than the cross-section of the magnetic circuit which is traversed by the alternating current flux.

25. In combination, an alternating current supply circuit, a first saturable core device having an alternating current winding and a direct current saturating winding, means for supplying current to said direct currentwinding, rectifying means, a core having magnetic characteristics similar to those of a portion of said first saturable core device, a winding on said core, a bridge circuit including said winding and the alternating current winding of said first saturable core device, means for energizing said bridge circuit from said alternating current supply circuit across one diagonal, means for energizing said rectifying means from another diagonal of said bridge, means for causing said bridge to be balanced when no direct current excitation is applied to said first saturable core device, a second saturable core device having an alternating current winding and a direct current saturating winding, means for energizing said second alternating current winding from said supply circuit, means for energizing said second mentioned direct current saturating winding from said rec- 5 1 tifying means, an output circuit, and means for energizing said output circuit in accordance with an electricalcondition of said last mentioned alternating current winding, whereby said second saturable core device is caused to receive satu- 10 rating excitation proportional to the difference between the alternating current flowing in said first mentioned saturable core device when said first mentioned device is subjected to a direct current saturating effect and the alternating curl5 rent flowing therein when no direct current saturating effect is applied thereto, said saturable core devices having cores so proportioned that the magnetic circuit which is traversed by alternating current magnetic flux is of greater dimen- 20 sions in said second saturable core device than in said first saturable core device.

26. In combination, an alternating current supply circuit, a saturable core device having an alternating current winding and a direct current 25 saturating winding, means for supplying current to said direct current winding, rectifying means,

a core having magnetic characteristics similar to those of a portion of said saturable core device, a winding on said core, a bridge circuit including 30 said winding and the alternating current winding of said saturable core device, means for energizing said bridge circuit from said alternating current supply circuit across one diagonal, means for energizing said rectifying means from another 35 diagonal of said bridge, means for causing said bridge to be balanced when no direct current excitation is applied to said saturable core device, an electromagnetic device having a direct current exciting winding, means for energizing said 40 exciting winding with uni-directional current from said rectifying means, means actuated in accordance with the magnetization of the core of said electro-magnetic device, whereby said electro-magnetic device is caused to receive exci- 45 tation proportional to the difference between the alternating current flowing in said saturable core device when said saturable core device is subjected to a direct current saturating effect and the alternating current flowing therein when no 50 direct current saturating effect is applied thereto.

2'7. A magnetic amplifying system comprising an alternating current input circuit, an alternating current supply circuit for supplying power of a frequency higher than that of said input, a 56 magnetic amplifier comprising a plurality of sat urable core devices, connected in cascade, each havinga saturating winding and an output winding, means for energizing said output windings from said supply circuit, a circuit including rec- 60 tifying means interconnecting the output winding of each device with the saturating winding of the next successive device, means connecting said input circuit to energize a saturating winding of said magnetic amplifier with uni-directional 65 current fluctuating in accordance with the frequency with said input, an output rectifier connected to rectify the output of said magnetic amplifier, a work circuit, and means including said output rectifier for supplying said work circuit with amplified energy of the frequency of said input and related thereto in magnitude.

28. A magnetic amplifying system comprising, an alternating current input circuit, an alternating current supply circuit for supplying power of a frequency higher than that of said input, a magnetic amplifier comprising a plurality of saturable core devices connected in cascade, each having a saturating winding and an output winding, means for energizing said output windings from said supply circuit, a circuit including rectifying means interconnecting the output winding of each device with the saturating winding of the next successive device, and means for substantially eliminating the effect on the last of said saturable core devices of the magnetizing current of any other of said devices, when unsaturated, comprising means associated with each device after the first for neutralizing the saturation thereof due to the magnetizing current of the preceding device, means connecting said input circuit to energize a saturating winding of said magnetic amplifier with uni-directional current fluctuating in accordance with the frequency of said input, an output rectifier connected to rectify the output of said magnetic amplifier, a work circuit, and means including said output rectifier for supplying said work circuit with amplified energy of the frequency of said input and related thereto in magnitude.

29. A push-pull alternating current magnetic amplifying system comprising, an alternating current input circuit, an alternating current supply circuit for supplying power of a frequency higher than that of said input, a pair of magnetic amplifiers, each of said amplifiers comprising a plurality of saturable core devices, connected in cascade, each having a saturating winding and an output winding, means for energizing said output windings from said supply circuit, a circuit including rectifying means interconnecting the output winding of each device with the saturating winding of the next successive de vice, a pair of input rectifiers connected in opposite sense and energized by said alternating current input, means for energizing a saturating winding of each of said magnetic amplifiers with unidirectional current from each of said last mentioned input rectifiers, whereby each of said amplifiers is subjected to a saturating effect alternately in accordance with successive input half cycles, a pair of output rectifiers connected to rectify the outputs of said magnetic amplifiers, a work circuit, and means for connecting said output rectifiers effectively in parallel to'supply 5 said work circuit with amplified alternating current energy of the frequency of said input and related thereto in magnitude. 30. A push-pull alternating current magnetic amplifying system comprising, an alternating 10 current input circuit, an altematlng current supply circuit for supplying power of a frequency higher than that of said input, a pair of magnetic amplifiers, each of said amplifiers comprising a plurality of saturable core devices, con- 15 nected in cascade, having a saturating winding and an output winding, means for energizing said output windings from said supply circuit, a circuit including rectifying means inter-connecting the output winding of each device with the saturating winding of the next successive device, and means for substantially eliminating the effect on the last of said saturable core devices of the magnetizing current of any other of said devices, when unsaturated, comprising means asso- 2'5 ciated with each device after the first for neutralizing the saturation thereof due to the magnetizing current of-the preceding device, a'pair of input rectifiers connected in opposite sense and energized by said alternating current input, 80 means for energizing a saturating winding of each of said magnetic amplifiers with uni-directional current from each of said last mentioned input rectifiers, whereby each of said amplifiers is subjected to a saturating efiect alte ately in accordance with successive input half cycles, a pair of output rectifiers connected to rectify the outputs of said magnetic amplifiers, a work circuit, and means for connecting said output rec- 40 tifiers effectively in parallel to supply said work circuit with amplified alternating current energy of the frequency of said input and related thereto in magnitude.

ALAN S. FITZ GERALD. 

